A NEW PASSIVE CONFINEMENT MODEL FOR THE ANALYSIS OF CONCRETE STRUCTURES SUBJECTED TO CYCLIC AND TRANSIENT DYNAMIC LOADING

The paper describes an analytical model for reinforced concrete members subjected to cyclic or transient dynamic loading. Model characterization is given in the context of a pseudo-spatial description of the stress state. This comprises a procedure for calculating and continuously updating the transverse confinement stress for a given applied axial strain, thus accounting for the passive confinement which an element of concrete is subjected to within a structural member. Comparison with existing uniaxial models shows that the new formulation takes note of previously neglected effects, such as non-coincident peaks of the steel and concrete stress-strain curves, and Poisson's ratio variation during loading. Moreover, comparison with 3D concrete constitutive relationships indicates that the level of accuracy is comparable, whilst significant computing time saving is achieved by the new model. Model validation is confirmed by comparison with cyclic loading laboratory test results. Finally, two frames with the same overall strength enhancement factor are analysed under earthquake loading; the difference in the response clearly demonstrates that the model accounts for important behavioural characteristics which are hitherto neglected in comparable existing models.